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go 迭代string數(shù)組操作 go for string[]

更新時間：2020年12月24日 10:31:28 作者：EasternUnbeaten

這篇文章主要介紹了go 迭代string數(shù)組操作 go for string[]，具有很好的參考價值，希望對大家有所幫助。一起跟隨小編過來看看吧

go 迭代string數(shù)組,直接拷貝去用即可

package main
import (
"fmt"
)
func main() {
  subsCodes := []string{"aaaa", "vvvvv", "dddd", "eeeee", "gfgggg"}
  for _, s := range subsCodes {
    fmt.Println(s)
  }
}

補(bǔ)充：golang字符串string與字符數(shù)組[]byte高效轉(zhuǎn)換

string與[]byte的直接轉(zhuǎn)換是通過底層數(shù)據(jù)copy實(shí)現(xiàn)的

var a = []byte("hello boy")

var b = string(a)

這種操作在并發(fā)量達(dá)到十萬百萬級別的時候會拖慢程序的處理速度

通過gdb調(diào)試來看一下string和[]byte的數(shù)據(jù)結(jié)構(gòu)

(gdb) l main.main
import (
  "fmt"
)
func main() {
  s := "hello, world!"
  b := []byte(s)
  fmt.Println(s, b)
(gdb) b 11
Breakpoint 1 at 0x487cd9: file /export/home/machao/src/test/strbytes.go, line 11.
(gdb) r
Starting program: /export/home/machao/src/test/test1 
Breakpoint 1, main.main () at /export/home/machao/src/test/strbytes.go:11
  fmt.Println(s, b)
(gdb) info locals
s = {
str = 0x4b8ccf "hello, world!level 3 resetload64 failednil stackbaseout of memorys.allocCount=srmount errorstill in listtimer expiredtriggerRatio=unreachable: value method xadd64 failedxchg64 failed nmidlelocked= on "..., len = 13}
b = {array = 0xc4200140e0 "hello, world!", len = 13, cap = 16}
(gdb) ptype s
type = struct string {
 uint8 *str;
 int len;
}
(gdb) ptype b
type = struct []uint8 {
 uint8 *array;
 int len;
 int cap;
}

轉(zhuǎn)換后 [ ]byte 底層數(shù)組與原 string 內(nèi)部指針并不相同，以此可確定數(shù)據(jù)被復(fù)制。那么，如不修改數(shù)據(jù)，僅轉(zhuǎn)換類型，是否可避開復(fù)制，從而提升性能？

從 ptype 輸出的結(jié)構(gòu)來看，string 可看做 [2]uintptr，而 [ ]byte 則是 [3]uintptr，這便于我們編寫代碼，無需額外定義結(jié)構(gòu)類型。如此，str2bytes 只需構(gòu)建 [3]uintptr{ptr, len, len}，而 bytes2str 更簡單，直接轉(zhuǎn)換指針類型，忽略掉 cap 即可。

通過unsafe.Pointer（指針轉(zhuǎn)換）和uintptr（指針運(yùn)算）實(shí)現(xiàn)轉(zhuǎn)換

package main
import (
  "fmt"
  "strings"
  "unsafe"
)
func str2bytes(s string) []byte {
  x := (*[2]uintptr)(unsafe.Pointer(&s))
  h := [3]uintptr{x[0], x[1], x[1]}
  return *(*[]byte)(unsafe.Pointer(&h))
}
func bytes2str(b []byte) string {
  return *(*string)(unsafe.Pointer(&b))
}
func main() {
  s := strings.Repeat("abc", 3)
  b := str2bytes(s)
  s2 := bytes2str(b)
  fmt.Println(b, s2)
}

沒有出現(xiàn)逃逸現(xiàn)象

package main
import (
 "testing"
 "io/ioutil"
 "time"
 "fmt"
)
var s, _ = ioutil.ReadFile("mydata4vipday.720.datx")
func test() {
 b := string(s)
 _ = []byte(b)
}
func test2() {
 b := bytes2str(s)
 _ = str2bytes(b)
}
func BenchmarkTest(b *testing.B) {
 t1 := time.Now()
 for i := 0; i < b.N; i++ {
   test()
 }
 fmt.Println("test", time.Now().Sub(t1), b.N)
}
func BenchmarkTestBlock(b *testing.B) {
 t1 := time.Now()
 for i := 0; i < b.N; i++ {
   test2()
 }
 fmt.Println("test block", time.Now().Sub(t1), b.N)
}

對比一下優(yōu)化前后的性能差異